CDC Telebriefing Transcript

West Nile Virus in the United States

August 7, 2003

DR. GERBERDING: I'm here today to provide an update on the West Nile
Virus outbreak that we are experiencing in the United States and to present
you some of the latest facts and figures. But please do keep in mind, as we
go forward, that the numbers are starting to change very, very quickly, so
you'll need to check our website for the most up-to-date information as we
go forward.

We are still working, of course, with our partners in the state and local
health agencies to detect cases of West Nile and also to initiate the
appropriate public health response. We recognize that the disease is hitting
especially hard in some new areas this year, and for the people who are
experiencing this for the first time, this is a real tough and difficult
situation.

So you have our support, and we of course also are extending our support
to the loved ones of the families who have lost people from West Nile or
those who are experiencing the difficulties of supporting a loved one who is
seriously ill.

The number of West Nile cases in the United States has actually tripled
since last week, so we are beginning to see a significant uptick in the
number of human individuals affected. So far 153 people are reported with
West Nile Virus infection from a total of 16 states. That includes 72 people
from Colorado, 19 people from Texas, 15 people from Louisiana, and several
people from the remaining 13 states.

We also officially have information about four deaths--two in Texas, one
in Alabama and one in Colorado--and we're aware of news reports that may
suggest that additional people have died from West Nile Virus infection.

There are some things about the epidemic this year that make it a little
bit different from last year. The median age for the people in the diagnosed
category this year is 45 years of age, which is actually slightly younger
than it was a year ago, where the average age was about 55 years.

And so far this year, all of the cases, all 153 cases of West Nile Virus
infection, have been attributable to mosquito bites, so we are not seeing
information suggesting that some other mechanism is contributing at this
point in time. And keep in mind that we are, of course, screening the blood
supply since July for West Nile and pulling any units that are suspicious
for infection. So we are doing what we can to protect the blood supply in
this country.

Now, I'm going to draw your attention to a couple maps over here, which I
think makes some very important points.

First of all, this map here in the center is the picture of states in the
United States who reported human West Nile Virus infection and animal West
Nile Virus infections as of August 7th, one year ago. So the blue states
here, the light-blue states, are those that had reported animal activity
only, and the states with the hatches are those that by this point in time
last year had reported human cases of West Nile. In fact, they had reported
112 human cases from four states. Louisiana was leading the nation at that
point in time with I think a total of over 70 cases.

Now, if you compare that map to the situation that we're in already this
year [second map], again, the lightest states here are those that have animal infection
only, but in the darker blue states--there are 16 all together--we are
reporting human cases.

So what these two maps tell you is that there are more cases already this
year with human disease compared to the same time last year. And I think
this is one picture of the situation that we are very concerned about, and
it tells us that we need to really step up the effort to control mosquitoes
and to prevent mosquito bites.

So, to give you some very specific examples here, last year at this time
you could see that Colorado had no human cases of West Nile, and actually no
West Nile Virus activity at all. Whereas, this year it's leading the country
in the number of new cases.

New Mexico had no cases last year and now has two cases of human West
Nile Virus infection.

And although Ohio had the most cases last year by the end of the West Nile
Virus season, it is also having cases this year, has had a recent increase
in the number of cases, suggesting that it's certainly not going to be
immune from the problem, and we're very concerned about the fact that there
may be more cases on the horizon for a number of the cases that were harder
hit last year, not just those states that are new to the map.

All of this is changing very rapidly, and it's important, as I said
earlier, to continue to check with our website and to keep posted on the
developments as they do emerge over time.

Now, the last graphic I wanted to mention is this graphic over here,
which is last year's picture of West Nile Virus infection. And right here,
where the red arrow comes down, is where the epidemic curve had evolved by
the same time last year. And what you can see is just after the end of the
first week of August, there was a huge increase in the number of West Nile
cases in our country. In fact, 65 percent of the cases of the entire season
occurred in the subsequent six weeks.

So that is very concerning to us. It indicates that we are starting the
epidemic with more cases and more areas affected last year, and if the same
pattern proves to hold true, we could be seeing an even greater number of
affected people.

So the very important message in all of this is the time to take action
is now. The time for people to really be conscientious about taking the
steps necessary to protect themselves from mosquito bites is right now and
to continue those activities throughout the rest of the summer season, and
although we haven't reported infection activity yet in the furthest West
states in the United States, we certainly don't want to be lulled into any
kind a sense that those states would be immune because we know that this
mosquito and this virus are on the move and therefore no one can be assumed
to be exempt.

Now there are also some warning signs by the surveillance that CDC does
in other animal populations.

We know that the reports of West Nile virus infection in horses, for
example this year, far outpaces the number of infected horses that we saw
last year, and we also have more than twice as many samples of mosquitoes
this year showing evidence of infection, and in some areas of the country,
in particular, up here in the Northeast, we're seeing just in the last week
a significant increase in the mosquito populations that are carrying the
virus.

For example last week, in New Jersey, of the various samples of
mosquitoes that we tested, we didn't find any, and this week all of the
samples came back positive.

So it indicate that this is truly following the seasonal pattern that we
saw last year and that people living in these affected areas need to be very
aggressive about taking steps to protect themselves.

So let me just review again what those protective measures are because
they're very, very important.

It's very important to use an insect repellant that contains DEET. DEET
is the chemical that keeps the mosquitoes from being attracted to human
skin.

If you see mosquitoes flying around your skin but they're not biting you,
it means the DEET is still working and you should be very careful about
following the instructions on the device or the product that you're using,
to know when you should reapply the DEET and how much you should use.

It's also important to know that you can find very detailed information
about insect repellents on the CDC Web site at www.cdc.gov .

There are some things you can do to mosquito-proof your home as well and
certainly screens are a very important part of that, but emptying the
standing water in your yard, and that includes water in bird baths and
flower pots, old tires, Coke cans, whatever you might have laying around on
your property, if you eliminate those standing water sources you eliminate
the place where mosquitoes breed, and since they don't have a wide range of
travel, it will help reduce the mosquito population on your own property.

We're going to be sending out some additional supplemental materials to
help spread the word about fighting the bite in local jurisdictions through
public service announcements, and so forth.

So as we understand that new jurisdictions are affected, we'll try to
provide that updated information and also local health agencies and state
health agencies are really a critically important portal of information,
particularly as it might pertain to efforts that could be underway in the
community to contain mosquitoes or to use larvicides or other sprays to
reduce the adult mosquito population.

So as I said, this news that we've presented here today is a reflection
of, I think, the complexity and thoroughness of our ability to detect West
Nile virus activity across our country, but also gives us a strong message
that this problem is certainly not in any better shape this year than it was
last year, and in fact the signs indicate that we could be in for a very
serious affliction this summer if we don't take steps to educate our public
and to get people to really fight the bite.

So thank you for your attention. I'm happy to take some questions.

QUESTION: Dr. Gerberding, I'm John Shurik [ph] with WXIA-TV, Atlanta. As
you said, these numbers are changing rapidly.

We understand that Georgia is now reporting a human case of West Nile
virus infection. So I guess that would change the number of states to
seventeen.

DR. GERBERDING: Let me explain a little bit why sometimes you hear things
in the local press that we don't have represented up here on our map.
Because this is a part of a national surveillance system and, as many of you
know, CDC does not report cases officially until the state health
departments have confirmed that they represent true infection, and whenever
a new state is involved or when a state has its first cases, we take extra
steps in the laboratory to be absolutely sure that it's truly West Nile
virus infection and not some other virus that can be confused with it.

So there's often a delay and, you know, we will certainly be adding
Georgia to the list, if indeed the test is confirmed to be true.

QUESTION: And to follow up, if I may, to what degree are the increases in
numbers attributable to doctors being encouraged to test and report, perhaps
milder cases that they might not have tested before?

DR. GERBERDING: Yes, because we do have better tests available to us this
year, it is possible that we are making an earlier diagnosis or that we are
picking up people who are less seriously ill. Overall, there are two main
forms of West Nile virus infection. The encephalitis or the brain
inflammation is the form that is the most serious and tends to be most
common in older people and is disproportionally included in the people who
die from West Nile infection.

But West Nile fever is also an important manifestation, less serious, may
not involve hospitalization but can be diagnosed with the same test.

This year, about half of the people with West Nile virus infection that
we've reported so far have the encephalitis. Last year, a few more people in
the included group had encephalitis, suggesting that we were not picking up
as many of the milder forms last year. So there could be some bias in the
numbers associated with capacity to pick up milder cases.

But even with that caveat, I think we're still seeing a major increase in
West Nile virus activity and it is extremely important that we take all the
steps necessary to contain it.

A question here.

QUESTION: April Nelson from CBS 46. Why is this time of year more
dangerous than the other months have been this summer?

DR. GERBERDING: There are several factors that influence the biology of
West Nile infection and mosquito transmission. Certainly, the climate is a
very important component of that. In the winter, it's just simply too cold
for mosquitoes to be active in most parts of our country, so they go into a
pause state where they're not feeding, they're not breeding, and they're not
infecting birds or other mammals.

It's also a process where a cycle in nature gets set up, where mosquitoes
are carrying the virus, they infect birds, the virus can multiply in birds
and other animals, and then when the next mosquito feeds they pick up an
even larger dose of the virus, and so the cycle sort of expands, over time,
as the summer progresses, and we're just getting into the season where the
right combination of many mosquitoes, large concentrations of virus in the
hosts, and people are outside, coming in contact with mosquitoes, all those
factors just seem to come together this time of year and create this
somewhat predictable pattern.

So we can always anticipate that this will be the season. I think we're
hoping that maybe other factors would work against the West Nile virus this
year, including perhaps some immunity in some of the species of animals or
birds that would serve as hosts. But what we're seeing is that if there is a
protective effective from exposure last year, it's certainly not good enough
to completely stop the transmission cycle.

I was wondering if you could explain, once again just clarify these
numbers on what percentage of those reported to have West Nile infection
have encephalitis and is it proportionally larger than last year, or in
absolute numbers larger than last year?

That was one thing and then the other question was what factors may be at
play? What hypotheses do you have about why Colorado is reporting so many
cases, after having no activity at all last year? Thanks.

DR. GERBERDING: Yes. Last year, about two-thirds of the patients with
West Nile infection had encephalitis. This year, at the present time, about
one-half of the patients have encephalitis. You know, this is very early,
and I would not draw too many conclusions for those numbers because people
who have fever today may be diagnosed with encephalitis tomorrow, and so we
need to understand, as always with any evolving epidemic, that those
patterns my be premature, and we don't have the data yet to draw any firm
conclusions about how this will look when it's all played out.

Your second question about why Colorado and why now, I think this is
again a pattern that we anticipated based on the movement of West Nile West
last year. Although at this time last year, Colorado did not have any
evidence of West Nile activity, by the end of the season, there was
activity. And so it meant that by the end of the year, some animals, and
mosquitoes or birds in Colorado had been exposed to the virus.

And so as bird migration happens and the cycle speeds up, it's not
surprising that we would see infection there. And because it's a new state,
it may follow the pattern we saw last year, where, for example Louisiana was
a new state for West Nile activity, and so they had a particularly difficult
summer with a large number of cases.

But as we say often, we cannot look into our crystal ball, and so
sometimes these things are better understood in retrospect than they are as
we go forward. We can't make any projections yet about who ultimately will
have the biggest problem or what states ultimately will have the most number
of cases.

Let me take a question from the phone, please.

OPERATOR: And for those on the phone, a quick reminder, if you do have a
question, please press star one.

And we'll go to the line of Miriam Falco with CNN. Please go ahead.

QUESTION: Hi, Dr. Gerberding. Thanks for having this.

My question is a little bit similar to what was just asked. Do you think
the fact that there are 72 cases in Colorado now is part of this cycle; the
fact that there were some mosquitoes in Colorado last year, and thus it's
easier to spread? And what predictions, without having the crystal ball, do
you see for the states like Illinois and Ohio that were hardest hit last
year?

And what information can you provide to the states that's different from
what was disseminated last year? Are there new PSAs? I mean, essentially the
information would be the same as you were giving out last year, would it
not?

DR. GERBERDING: Yes. Again, I can't predict what will happen in Colorado
as the season unfolds, nor can I completely explain it this time why they
are seeing the largest number of new cases. Of course, any reported illness
is dependent on the actual frequency of the illness, stability of clinicians
to diagnose the illness and the sensitivity of the reporting system. And we
know that the efforts that have been in place for several years now, to
enhance all of those capacities in the states, do seem to have paid off. So
we are seeing very good reporting of West Nile infection.

The advice on how to protect yourself against West Nile Virus infection
hasn't changed from year-to-year. We are very vigorous in recommending that
people take the steps necessary to reduce mosquito bites and to reduce
mosquito breeding on their property, but we don't have any new tools in our
took kit to help protect people.
What we do have new this year is some very important advance in the field of
the diagnostic testing, and particularly in our ability to protect the blood
supply, and in addition the work that the NIH has moved forward in terms of
developing a vaccine for West Nile, but we're not going to have a vaccine in
time to make any difference this year. So it's the old-fashioned method of
reducing mosquitoes and reducing mosquito bites that we have to rely on.

Let me take another question from the phone, please.

OPERATOR: And that will be from James Erickson, Rocky Mountain News.
Please go ahead.

QUESTION: Hi. When I ask health officials out here why we're seeing so
much West Nile activity in Colorado, I get two answers. The first is that
this is the second year the virus has been in the state, and West Nile often
hits hard the second year. You've already alluded to that.

The other answer I get is that the rainstorms here have been ideally
timed this spring and summer to produce lots of mosquitoes.

I'm wondering what other factors could be contributing to this outburst.
For example, is this telling us something about the competence of Culex
tarsalis as a vector for West Nile?

DR. GERBERDING: One of the unfortunate aspects about the West Nile Virus
is that it's not very picky about its host. It affects an extremely broad
range of birds, it affects an extremely broad range of mammals, and it
affects an extremely broad range of mosquitoes. So while it may have a
particular favorite mosquito host in a given geography, it's not picky, and
that's one of the reasons why I think, at least one of the hypotheses about
why it's been able to spread so quickly across the United States, because it
can enter a whole variety of hosts and mosquito vectors.
Therefore, something that caused a reduction or a downturn in one
population, doesn't have much impact on the overall life cycle of the
mosquito.

But you do bring up an important issue, and that is the issue of weather.
We know that climate is an additional variable that has a big impact on bird
migration patterns, as well as mosquito breeding, and so it is certainly
possible that in a particularly rainy season or where there is a great deal
of water standing that allows more mosquito breeding, that would be a worse
year for mosquito populations and all of the mosquito-borne diseases.

What do you make of the reduction in the median age of those affected
this year compared to last?

DR. GERBERDING: It's too early to draw any conclusions about the age
distribution overall. One factor that might be accounting for that is the
fact that we are including people with less-severe disease in a slightly
greater proportion this year than last year. And because the older you are,
the more likely you are to get the encephalitis form of West Nile Virus
infection, if we're picking up less serious disease, then we may be picking
up more disease in younger people, and that's changing the distribution a
bit.

But, again, we have people of all age groups represented in the epidemic
so far, and we can't conclude that anybody is immune from even the most
severe form of infection.

I would just add to that that because it is the elderly population that
is at the highest risk for the encephalitis, it's especially important that
our seniors take the steps necessary to repel mosquitoes or to wear
long-sleeve clothing and long pants when outdoors because this could be an
especially serious medical issue for you.

I'm sort of wondering about the efficacy of the prevention program that
we have in place here. You know, you came out last summer full throttle with
this Fight the Bite program, and I'm not sure how well that was broadcast in
Colorado, but even in the face of this strong prevention plan, we've got
this huge outbreak in Colorado, and we're asking people in the summer to
wear long-sleeve clothing and long-sleeve pants. Is it really working, and
is there anything else you're working on in its place that might be more
effective?

DR. GERBERDING: Preventing West Nile Virus infection is a multifactorial
process, and of course mosquito control is a huge component of that. One of
the reasons why we make these investments in tracking the mosquito or the
virus in mosquitoes, and birds, and animals is so that we can anticipate
where the next human cases will be. And when a jurisdiction knows that it
has the virus in that area, then there are additional steps that officials
may need to take that help reduce the threat to human health. And those
steps include using larvicides to kill mosquitoes as they are hatching in
the breeding ground, as well as, in some cases, if the problem can't be
controlled that way, decisions about spraying for adult mosquitoes may need
to be considered.

So it's a comprehensive process. But no matter what your jurisdiction is
doing or is able to do or what makes sense to do in a particular location,
there's always a role for personal protection.

You've asked is it enough and is it making a difference. It's kind of the
dilemma of all prevention activities, is that it's very difficult to show
what you've prevented. You can only show what's left over after all of your
prevention impact has been accounted for.

So I believe that the information we have so far indicates that a
comprehensive vector control program is a very important strategy and is
important in reducing mosquito populations and reducing risk, but in
addition, we know that mosquito repellents work, and the other measures to
reduce the possibility of a bite are very, very important.

So we don't want people to think, oh, well, it's not making a difference.
If anything, this is an indication to step up to do those things even more
rigorously before, and not to forget that the West Nile season goes on for a
long time. Last year it went clear through October. So it's not just a
question of when it's summer vacation. It's a question for the summer and
the fall.

A question here.

QUESTION: I'm Daniel Yee with Associated Press.

So what are the challenges this year for dealing with a virus that's here
to stay?

And, secondly, have you had any requests from states for CDC assistance?

DR. GERBERDING: The challenges this year are really the same as the
challenges every year, and that is anticipate where the problem is going to
emerge, act proactively in those jurisdictions to do the appropriate things
to reduce the threat to human health, to do everything possible to protect
the blood supply, to inform people. Clearly, the more you know about
protection, the better of you are, in terms of making personal health
decisions for you or your family.

CDC has already provided to the states a great deal of funding to support
West Nile prevention activities. It's been an ongoing program, we scaled it
up last year and we're continuing to do everything we can, not only to
provide money to state and local health agencies but also to track the
problem and to make this whole ARBONET, this is called, our surveillance
system, to make it as useful and as timely as we can to people in those
jurisdictions.

If you're interested in specific dollar amount for our funding, we can
make that information available to you through our press office.

QUESTION: I guess there've just been Epi teams and stuff?

DR. GERBERDING: Yeah. So far, we have not received requests for specific
Epi aids on behalf of West Nile. I will say that in Colorado, one of our
large CDC components if physically located in Fort Collins, Colorado, and
that happens to be our division that deals with West Nile virus infection.
So there is actually a great deal of interaction with CDC in Colorado and
the state and local health officials there, so it is not a sign of anything
other than so far, the states are well-prepared and are able to manage the
situation without additional technical support from CDC.

QUESTION: Yes; hi. Last year, it seemed that most of the cases,
especially in Illinois and other parts of the Midwest, were clustered in
urban/suburban areas. I can't see your maps but I'm wondering, with cases
being reported this year, is that following a similar trend?

DR. GERBERDING: I believe your question was are we seeing a tendency
toward more cases in urban and suburban areas?

QUESTION: Yes--

DR. GERBERDING: Was that your question?

QUESTION: [inaudible].

DR. GERBERDING: Yes. We actually track the affected counties that are
reporting West Nile virus activity and there always is a tendency to see
more human cases in the areas that have a greater density of population, so
that's one of the explanations for that distribution.

But the rural areas are certainly not immune, as we've seen in the animal
populations and in some of the human people who have been affected in other
parts of the country this year, so it's too soon to tell what the overall
distribution will be as this moves forward.

Do I have another question from the phone, please.

MODERATOR: And that's Rob Stein, Washington Post. Please go ahead.

QUESTION: Yeah. Hi, Dr. Gerberding. Thanks for doing this. You might have
had these numbers on the slide that you showed but I couldn't see them over
the phone. I was just wondering if you had the equivalent numbers for this
time last year, how many cases, how many human cases, how many deaths, and
how many states were affected this time last year?

DR. GERBERDING: Yes. Last year, at this time, we had a total of 112 cases
in four states. This year, we have 153 human cases in 16 states, and if you
want additional breakdown in terms of reported deaths and what those states
were, we'll be happy to provide them to you, so you can just get in touch
with the CDC press office.

I'll take another telephone question, please.

MODERATOR: And that's from Anita Manning, USA Today. Please go ahead.

QUESTION: Hi, Dr. Gerberding; thank you for doing this.

I have a couple of sort of unrelated questions. One of them is you
mentioned that the blood supply is being screened and has been since early
July, and I'm wondering how often West Nile virus is being picked up in
donated blood?

And then I also wanted to ask if there's anything different about the
mosquitoes that are out West, that's causing the locus of this epidemic to
move West as it has been?

DR. GERBERDING: The blood supply is being screened for West Nile virus
infection using a test that was created very quickly and represents, I
think, a heroic achievement on the part of the blood banking industry as
well as the FDA to get this out in such a short period of time.

The test is very sensitive and that means that it will detect many cases
of possible West Nile virus infection that may not actually represent true
infection.

But that's exactly the way we want it to work. If there is the positive
screening test in the blood, those units of blood product are immediately
pulled so that they don't get transfused into people, and then we take our
time sorting out whether they represent true infections and whether the unit
actually had live virus in it or not.

So there have been units of blood pulled. We reported, some time ago, the
first confirmed unit of blood that was pulled from the blood supply and what
we're doing right now is carefully evaluating the pulled units to see
whether or not they would have posed a threat if they had been transfused,
and we're looking to see whether or not that information about pulled units
is an additional marker of where the virus activity is, that would help us
understand even better where a threat to human health resides.

So we will be providing you updated information as the full assessment of
the pulled units of blood gets completed.

QUESTION: Is there any sense--thanks for doing this, by the way. Is there
any sense of how effective the tests are? Do we have any more information
about that, the Roche and Chiron test?

DR. GERBERDING: The tests are very good, again, at screening for West
Nile virus infection but the definitive test is something I believe called
the plaque neutralization assay which really takes a while to complete.

Am I right in that? Did I get that terminology correct?

That is a test that really relies on the virus to actually grow up and to
be definitively distinguished from other viral agents that it can be
confused with.

So the gold standard test is still a test that is done primarily by CDC
in Fort Collins, and we don't have to use that gold standard test all of the
time because once we know that the virus is in the jurisdiction, if the
screening test is positive and the patient's clinical signs and symptoms are
compatible with West Nile, the commercially available tests tend to perform
extremely well.

But we will be looking at that as we go forward this year and really
being able to conduct a much more thorough assessment of the reliability of
the new tests that are being used for diagnostic purposes.

In cases where there's a discrepancy between the screening test in a
commercial laboratory, we always encourage that the test be reevaluated by
the state health department laboratory and then referred to CDC, if
necessary, to clear that up.

Let me just take one more question from the phone, please.

Is there one more question from the phone?

MODERATOR: Yes, from the line of Paul O'Niece [ph] with WCBS-TV. Please
go ahead.

QUESTION: Dr. Gerberding, thank you for taking our questions.

A point of clarification here. You mentioned this rapid test used for
blood. A rapid test is also being used for human cases; is that correct?

DR. GERBERDING: That's correct.

QUESTION: Now how is the rapid test affecting the numbers that we're
talking about? Is it possible that we're seeing more numbers, this 153,
because the tests results are coming back faster?

DR. GERBERDING: No. The number of cases here cannot be related totally to
the speed of the testing, although we are likely to be able to rule in cases
more quickly than we were in the past.

The testing of the blood is not something that's reflected in the case
count here. That would be a separate surveillance system.

Finding the virus in the blood of a blood donor does not meet the case
definition for West Nile virus infection. So that's why we are counting
those separately.

So these numbers are not inflated for individuals that could be picked up
by screening the blood supply. But, again, these numbers are going to change
over time.

We want you to be aware of the fact that while we expect, unfortunately,
we'll be seeing more cases of West Nile, that we are constantly evaluating
the performance of the test, and beginning to understand the broader
clinical picture of this illness, and we certainly will anticipate updated
information and a more accurate view of the scope and magnitude of the
problem as we go forward.

The bottom line is that it's here, it's happening in a lot of
jurisdictions, every sign indicates that it's on the increase and now is the
time for people to step up their efforts to fight the bite.